1. Field of the Invention
This invention relates to a roller assembly for conveying a sheet-shaped workpiece in an electroplating apparatus, more particularly to a roller assembly, which is provided with at least one pair of guiding members for guiding the workpiece to move therebetween, thereby permitting accurate formation of a metal coating on target areas of the workpiece.
2. Description of the Related Art
Referring to FIG. 1, a conventional electroplating apparatus that is used in an automated manufacturing process of a printed circuit board is shown to include pairs of conducting rollers 7 disposed at upstream and downstream sides of an electroplating bath 9, which contains an electrolyte. A plurality of spray tubes 91, 92 and roller units 93 are provided inside the electroplating bath 9. The spray tubes 91, 92 not only function as anodes as they are connected electrically to a power source, but also spray an electrolyte onto a horizontal circuit board 8. Each of the roller units 93 includes a plurality of upper rollers 931 and a lower roller 932 to advance the board 8 through the electroplating bath 9. The upper rollers 932 are arranged such that they will move downward by virtue of gravity to place the lowermost upper roller 931 in contact with the corresponding lower roller 932 as soon as the board 8 moves past the inlet 94 and outlet 94 of the electroplating bath 9, thereby sealing the inlet 94 and the outlet 94 and preventing the electrolyte from leaking and staining the conducting rollers 7 provided outwardly of the electroplating bath 9.
The disadvantages of the aforesaid electroplating apparatus are as follows:
(1) A photosensitive film is applied to a surface of the board 8 prior to electroplating. Hence, the surface of the board 8 has a film area to be electroplated, and a bare copper area for contact with the roller units 93. Because no guiding means is provided for guiding the bare copper area of the board 8 to move in a direction that is perpendicular to the rollers 931, 932, the roller units 93 often press on the film area. As a result, it is difficult to form a desired circuit pattern on the board 8.
(2) A resistance loss is incurred on the conducting roller 7, and increases gradually from one end to another end in view of the condition that only a single cathode current input is provided to one end of the conducting roller 7, thereby resulting in an uneven thickness of metal coating on the board 8.
An object of this invention is to provide a roller assembly for an electroplating apparatus, which is provided with at least one pair of guiding members, the positions of which can be adjusted automatically according to the width of a sheet-shaped workpiece so as to guide the workpiece to move therebetween, thereby permitting accurate formation of a metal coating on target areas of the workpiece.
Another object of this invention is to provide a roller assembly for an electroplating apparatus, which can supply cathode current simultaneously to two opposite sides of a sheet-shaped workpiece, thereby forming a uniform-thickness of metal coating on the workpiece.
According to this invention, a roller assembly for an electroplating apparatus includes a plurality of feeding rollers adapted to advance a sheet-shaped workpiece, and a threaded rod disposed parallel to the feeding rollers and having a left-hand thread portion and a right-hand thread portion. Two guiding members are respectively formed with two threaded holes, which engage the left-hand and right-hand thread portions of the rod. A sensing unit detects the width of the workpiece to activate a controller and a driving unit, which rotates the rod so as to move the guiding members in opposite directions such that the guiding members abut against two opposite sides of the workpiece, thereby guiding the workpiece to move therebetween. Two conducting units are attached respectively to the guiding members for supplying cathode current to the sides of the workpiece.